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During the past five to ten years, a variety of tools has been developed in the disciplines of both gene engineering, and molecular and structural biology. Some of these advances have permitted scientists not only to identify and characterize genes, but also to target these genes by disruption, thus eliminating their function in living animals, and to det- mine the biological responses to altered gene products. This has particular significance in endocrine systems, in which feedback mechanisms between the hypothalamus, pi- itary, and end organs are critical in normal physiology. Interpretation of the physiological significance, or the site of action of specific molecules in this context, has been difficult prior to transgenic technology. Major advances have occurred specifically in the areas of growth and development, and of reproduction. Coupled with analysis of naturally occurring mutations in humans, the use of transgenic animals and in vitro systems has recently allowed endocrinologists to understand the importance of specific thyroid hormone receptor isoforms in vivo, the molecular basis for generalized resistance to thyroid hormones via mutations in the nuclear receptor, and mechanisms for suppressing gene transcription. Previously designated “orphan rec- tors,” such as steroidogenic factor-1, were demonstrated to have critical roles in dev- opment and reproduction. Other nuclear receptors—including those for thyroid hormone, estrogens, androgens, and progesterone—were shown to bind to coactivator and co- pressor proteins that modified their transcriptional activity, and contributed to the ce- specific effects of the hormones.
Since the observation in the 19th century that an extract of the suprarenal bodies injected into the circulation caused a rise in blood pressure, the endocrine system has become a major component in our understanding of human physiology. The introduction of radioimmunoassay techniques and the ability to measure minimal amounts of hor mones (a term derived from the Greek "to excite") have shown that acute exercise causes a release of a large number of hormones and that chronic exercise may further lead to long-term alterations in endocrine homeostasis. Actually, almost every organ and system in the body is affected by physical activity and exercise, much of it through the endocrine and neuroendocrine system. Investigation ofthe effect of acute or chronic physical activity on the endocrine system is a complex matter since the stimulus called "exercise" has many components, such as mode, intensity, duration, and others. In addition, several other factors, such as age, gender, training status, body temperature, circadian rhythm, metabolic state, menstrual cycle, and various external conditions as well as psychological factors, can modify the effect of physical activity on hormonal secretion. Moreover, the physiol9gical stimulus of exercise often provokes several and parallel cascades of biochemical and endocrine changes. It is therefore often extremely difficult to distinguish between primary and secondary events and between cause and effect. These limitations will be discussed in Chapter 1.
Those who are familiar with the two volumes of The Year in Endocrinology may, at first glance, fail to recognize their relationship to the present volume, Contemporary Endocrinology. The name is different and the cover design different, but nonetheless the admonition against judging a book by its cover is very well taken in this instance. In fact, Contemporary Endocrinology is not only the direct linear descendant of The Year in Endocrinology, it is a purposeful clone thereof-the topics are unchanged, the talented group of authors is unchanged, and most importantly, both the objective of the work and the manner in which that objective is approached are unchanged. The objective is, of course, to assist the reader in maintaining currency with respect to important developments, both basic and clinical, in the major areas of endocrinology. We are all much too familiar, unfortunately, with the difficulty of maintaining currency these days. Our approach to dealing with the informational inflation that we are suffering is similar to that used by economists in dealing with monetary inflation, that is, to increase interest. This we have attempted to do by providing for the reader an easy-to-read group of essays in which advances in individual areas of endocrinology are re viewed broadly, synthesized, and placed into perspective by a group of authors who are authorities in their individual fields. They serve, not as guest artists, but as members of a stable Editorial Board that provides continuity by contributing to successive volumes.
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